docs: update README with repo URL, add setup guide and .gitignore

- Update README installation to use uv tool install with self-hosted repo URL
- Add docs/SETUP.md for AI agent consumption
- Add .gitignore for __pycache__, build artifacts, venv, IDE files
- Remove obsolete superpowers planning docs

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -0,0 +1,17 @@
+__pycache__/
+*.py[cod]
+*$py.class
+
+# Distribution
+dist/
+*.egg-info/
+*.whl
+
+# Virtual environments
+.venv/
+venv/
+
+# IDE
+.idea/
+.vscode/
+*.swp